Space-Time Communications

Space is fundamental to all wireless communication. Spatial diversity encompasses techniques for achieving high-data-rate wireless communications by exploiting the space in which that communication occurs.

Dish Array

Spatial diversity grew from the field of Microwave Radar Communications of the 1950s and 1960s, where many antennas were used to accurately locate and track distant objects. The field is governed by the principles of Information Theory, and motivated by the need for high-data-rate communication to small, mobile devices. The exploitation of spatial resources allows for increasing the number of mobile subscribers within a given cellular network, increasing the rate of data to each user and increasing the range of coverage, while reducing the size of the mobile devices and reducing device power usage. In addition, Spatial Diversity may be used to overcome channel distortion effects, such as are caused by high-speed movement of mobile users.

BLAST Chip

Multiple-Input Multiple-Output (MIMO) Wireless is a recent development within the field of spatial diversity which provides significant increases to wireless communication data-rates by using multiple

I. E. Telatar

antennas. The MIMO field grew through the application of Information Theory and the fundamental work by I. Emre Telatar (left), Gerry Foschini, and Michael Gans (all of whom worked with Bell-Labs at the time) and is now driving new technologies such as 4G mobile telephony. Very high data-rates -- such as required for wireless high-definition digital TV -- are within reach of mobile users thanks to MIMO. The theoretical results have already been developed into digital chip, such as the Bell-Labs BLAST chip shown above.

The area of space-time communications is still very much in development. The IEEE Transactions on Information Theory recently devoted the October 2003 special issue to space-time transmission, reception, coding and signal processing.

Spatial Diversity/MIMO timeline

Below is a brief time-line of spatial diversity, and MIMO. The red triangles indicate significant steps toward the current state-of-the-art in spatial diversity.

History of Space-Time Communications

Australian Bell Labs researchers D. Garrett (standing) and M. Bickerstaff verify that the BLAST chip is receiving data at 19.2 Mbps.

Key Research Challenges

The key research challenges for spatial diversity and MIMO include modelling of space in communications, developing fundamental theoretical limits to the resources space provides and producing technologies which exploit these resources. At present it is not clear how much information can be stored in a region of space, nor even how communication over a spatially diverse channel should be modelled in anything but the most simple and abstract arrangements. Advances in these areas are driving new technology, such as new handsets for mobile telephones, in addition to improving current technology. Specific projects may include